We saw a preview of an amazing little game called Halo:
That was running on a 500 MHz G4 with a 100 MHz bus, truly amazing stuff for the time.
Then as we all know, Microsoft bought the company and prostituted the product for their Xbox launch and screwed up the PC and Mac versions which had to be re-ported much later.
And now that MS finally finished digesting Bungie and has spit it back up, hopefully we'll see some great innovation with this next effort:
http://www.bungie.net/en-us/destiny